In an optical transmitter, a laser diode driver (LDD: Laser Diode Driver) that drives a laser diode (LD) is controlled, so that optical power of an optical signal output from the LD is maintained at a fixed value. Specifically, a method of providing a photo detector (PD: Photo Diode) for monitoring optical power emitted from the LD and controlling the LDD in response to an electrical monitoring signals output by the PD is known, (for example, see Japanese Patent Application Laid-Open No. 2011-239364).
Here, for example, 100 GbE CFP (100 Gigabit Ether C Form-factor Pluggable) optical transceivers have been introducing a configuration that a plurality of PDs is provided corresponding to a plurality of LDs and the electrical monitoring signals output from the respective PDs are received by ADCs (Analog Digital Converter) built in a controller. Such a configuration has a risk that the electrical monitoring signals output from the plurality of PDs interfere with each other (cause crosstalk). In this case, some noise occurred in the electrical monitoring signals prevents the LDD from being normally controlled, so that the optical power of the LD cannot be maintained at an appropriate value.
It can be considered to evaluate an effect of the crosstalk among the electrical signals beforehand and control the LDD by cancelling the effect of the crosstalk in practice. However such prior measurement needs to be performed for multiple patterns, so that processes of the evaluation and cancellation are complicated. For example, setting each of four LDs to ON (emission) or OFF (extraction) causes a combination of eight cases each to be handled differently.